Pyromellitic dianhydride is commercially available and widely used as the monomer for preparing a variety of linear, ladder, or crosslinked high-temperature polymers with excellent thermal, thermomechanical, thermooxidative and radiation resistances by polymerization with aromatic di- or polyfunctional amines. Linear polyimides, ladder poly(imidazopyrrolone)s and crosslinked polyesters and polyamides are representative Examples of such polymers. Polyimides are of particular importance and widely used in industry as thermally stable films, liquid crystal alignment layers, semiconductor coatings, or flexible printed circuit boards.
However, the poly(pyromellitimide)s prepared by polycondensation with aromatic diamines have only poor solubilities or fusibilities, and they have mostly been processed via precursor processing methods. To improve the processabilities of the polyimides, incorporation of organic substituents at 3- and 6-positions of pyromellitic dianhydride has been attempted and 3,6-bis(Q)pyromellitic dianhydrides have been developed, where Q is bromo, fluoro, chloro, trifluoromethyl, phenyl or oxyphenyl. In spite of the presence of these substituents, no distinctive improvement of the processability compared to poly(pyromellitimide)s has been observed.
Therefore, needs have been existed for the development of new pyromellitic dianhydride derivatives which provide, when polymerized with the same aromatic diamines, distinctively more improved processabilities of the polyimides than the unsubstituted poly(pyromellitimide)s or poly[3,6-bis(Q)pyromellitimide]s.